It may be related to the famous 301 view count where YouTube would stop updating the total pending further verification that the views are legitimate. See: https://youtu.be/oIkhgagvrjI This behavior was later removed in 2015, but I wouldn’t be surprised if something similar is happening here.

The app has been glitched recently and only shows the thumbs up count from the first video you've watched.

Maybe Hallucinations-as-a-Service?

Lot of people reporting similar months ago:

https://www.reddit.com/r/youtube/comments/15fvsu0/likes_are_...

Sounds like a caching bug in the app.

Maybe system updates counts when it reaches that number?

Cuz it adds up to 9